Xinput Extension Devices

[Jennifer Elaan]

Hi,
   I'm puzzled that Xinput 2 removes support for the concept of extension
devices that the original used.  For touchpads, styluses, and the like, the
new code makes perfect sense to me, but what about LPFK, Dials, SpaceBalls,
etc, that aren't meant to send pointer events?

   I ask because I have, and use, a SpaceNavigator.  The events it sends are
interpreted by applications that are aware of it.  Currently, the state of
SpaceNavigator support in Linux is rather fragmented - some applications
open it directly as an evdev device, some use the proprietary driver.  I
think that treating it as an extension device, as the original xinput design
appeared to support, is the right idea.  The focused application receives
the input events from it, allowing two open applications to share it.

   Floating slaves don't quite cover this use case.  Applications would have
to arbitrate for control, and since simply following the keyboard focus is
the desired behavior, this seems excessive.  Is it possible to support
extension devices as a third class of devices, as we currently have
keyboards and pointers?

   I'm up for writing and testing the SpaceNavigator driver itself (and I
have started already), but the modifications to xinput to support it are
nontrivial and I'm really out of my depth.

Thanks,
Jen.
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